The subject matter of the instant invention relates to coating compositions containing at least one silica or borate containing compound, methods for making the compositions and methods of using the compounds for treating a metal surface.
Electric motors and methods of manufacturing the same are well known. A core (also known as a rotor core) of the motor comprises stacked and coined together laminates. Each individual laminate defines a center opening for connecting a shaft and a series of evenly spaced openings around the periphery of the laminate. The openings can have any suitable configuration. The laminates are stacked and coined in a sequential and slightly offset fashion such that the openings around the periphery define a spiral channel passing along the longitudinal axis of the core/rotor. This channel passes along the longitudinal axis in a helix or spiral fashion that enhances the motor performance. The rotors cores are heat treated to form a surface comprising magnetite Fe3O4. After heat treating, the channels are injected with molten aluminum thereby encapsulating the rotor within aluminum. The aluminum is typically injected at a temperature of about 1,300 to about 1,400 F. and at a pressure of about 4,000 to about 6,000 psi.
There is a problem in this art associated with injecting the aluminum within the channels. It is believed that the aluminum can solder to the steel and form an electrical connection between the laminates, e.g., as detailed in xe2x80x9cA Description of the Functions and Process Tests For Cast Aluminum Induction Motor Squirrel Cage Rotorsxe2x80x9d by J. Johnson et al., presented as a paper at Rotor Technology ""86, Feb. 5-7, 1986, the disclosure of which is hereby incorporated by reference. Such an electrical connection can cause a short within the electric motor thereby reducing, if not eliminating, the effectiveness of the electric motor. There is a need in this art for an electric motor fabrication method that isolates the aluminum from the laminates e.g., prevents the molten aluminum from infiltrating between the stacked/coined laminates (with or without a magnetite surface).
There is also a need in this art to improve electric motor manufacturing by employing the principals known as xe2x80x9clean manufacturingxe2x80x9d in order to eliminate non-value added activities during the manufacturing process. Examples of non-value added activities are described in U.S. Pat. No. 5,161,597 (Dohoger) and U.S. Pat. No. 5,488,984 (Fahy), e.g., burn-off ovens, oxidation furnaces, hot drop, among other processing delays. By improving electric motor manufacturing and employing statistical process controls, the amount of work in progress can be reduced and xe2x80x9cjust in timexe2x80x9d production methods can be adopted.
As described in U.S. Pat. No. 5,488,984, rotors of electric motors can be coated with sodium nitrate. Other conventional coatings compositions and methods for treating metals are disclosed in U.S. Pat. Nos. 4,870,814; 4,032,366; 5,182,963; 5,776,261; 3,839,256; 3,372,038; 2,641,556; 2,803,566; 5,723,181; 2,554,250; 1,068,410; 2,811,473; 2,282,163; 3,910,797; 3,832,204; 3,917,648; 2,978,361; 5,789,085; 3,796,608; 3,133,829; 2,385,332; 2,799,658; 2,641,556; 3,839,256; and 3,752,689.
Magnetic Silicon Steels produced for use as laminates either for rotor, stator or transformer application typically require an annealing separator comprising thin films of inorganic compounds such as magnesium oxide and phosphate as taught by J. Evans in U.S. Pat. No. 3,615,918 and Akerblom in U.S. Pat. No. 4,120,702 and Nakayama U.S. Pat. No. 4,875,947 and magnesium from U.S. Pat. No. 2,385,332 V. Carpenter, and Steger in U.S. Pat. No. 3,583,887, sodium silicate Lee in U.S. Pat. No. 3,945,862 teaches an amorphous magnesia silica complex and a boron bearing compound. Evans teaches an insulation coating for electrical steels in U.S. Pat. No. 3,996,073 comprising an aluminum magnesium phosphate solution with colloidal silica and chromic anhydride. Organic quaternary ammonium silicate coatings are taught by R. Parkinson, U.S. Pat. No. 3,839,256 and polyvinyl acetate with phosphoric acid and chromic acid is taught by Kitayama in U.S. Pat. No. 3,793,073. Additionally, Yamazaki, in U.S. Pat. No. 5,961,744 teaches colloidal silica and aluminum phosphate. Haselkom in U.S. Pat. No. 4,496,399 teaches silica and aluminum silicate dispersed in vinyl resins, while Morito in U.S. Pat. No. 4,255,205 teaches silicate aluminum oxide, strontium and barium compounds in phosphoric acid. B. Perfetti in U.S. Pat. No. 4,507,360 teaches magnesium silicate, mica, titanium oxide and alkali metal borate. Perfetti also teaches in U.S. Pat. No. 4,517,325 the use of organic quaternary ammonium silicate and ethylene/acrylic or ethylene/vinyl/acetate copolymer a small amount of barium, strontium or lead chromate. Katayarna in U.S. Pat. No. 4,844,753 teaches acrylic and a acrylic styrene resins with chromates. Nakamura in U.S. Pat. No. 4,618,377 also teaches emulsions. U.S. Pat. No. 1,951,039 by Scharschu, teaches sodium silicate, lime and iron oxide. D. Loudermilk teaches inorganic/organic insulating films in U.S. Pat. No. 5,955,201 utilizing aluminum silicate, aluminum potassium silicate and magnesium silicate dispersed in a water-soluble, organic solvent, resin. Also acrylic resin with chromates are taught by K. Kenichi in U.S. Pat. No. 4,844,753. Also Robinson teaches a paint in U.S. Pat. No. 2,641,556 comprising refractory material suspended in a solution of a decomposable binder such as a solution of an alkyd resin, cellular acetate in organic solvents. U.S. Pat. No. 5,922,413 by Takeda, teaches a method of coating a rotor core by applying a liquid primer followed by applying a powder coat. The disclosure of the previously identified U.S. Patents and publications is hereby incorporated by reference.
The present invention relates to coating compositions and methods for using such compositions. The present invention solves problems associated with conventional electric motor manufacturing practices by providing inorganic and/or organic coating compositions applied to rotor cores to eliminate soldering during aluminum injection. These coatings can be applied upon rotor and/or stators laminates to enhance motor performance. These coatings can also be employed in transformers and other electronic components. The instant invention further solves problems associated with conventional electric motor fabrication methods by providing at least one film or layer of a coating composition within channels or bar slots defined by the rotor of the electric motor core/rotor (depending upon the design of the motor the slots can be defined within the rotor or open ended along the longitudinal axis of the rotor). The inventive coating composition is also typically applied upon all exposed surfaces of the rotor, e.g., within the channels and exterior surfaces of the rotor. The coated rotor is then contacted with a molten metal. The coating composition functions to isolate the laminates (e.g., steel) of the rotor from a molten metal (e.g., aluminum and its alloys), which surrounds the rotor and fills the channels thereby embedding the rotor, and prevents the metal from forming an undesirable conductive path typically termed soldering among the individual laminates.
In one aspect of the invention, the coating composition interacts or reacts with a molten aluminum phase, i.e., the molten aluminum that is injected into and around the rotor. That is, the molten aluminum can react in situ with at least a portion of the inventive coating to form a mixed oxide. By reacting with the molten aluminum, the inventive coating prevents the aluminum from adversely affecting (or contacting) an underlying metal containing surface. The mixed oxide or reaction product can also function as a barrier or shield to the underlying metal containing surface, e.g., silicon steel laminates.
The instant coating composition functions to not only isolate the channels from corrosion and/or corrosion erosion caused when the aluminum is injected into the channels and serves as a heat shield but also reacts with molten aluminum and other phases present during injection. In some cases, the coating can interact with the molten aluminum to form a layer having a distinct composition, e.g., a glassy or an amorphous layer. The layer can be comprised of at least one of silicate or at least one borate containing compounds, a complex oxide, complex iron-sodium silicates, aluminum potassium silicates, aluminum/silicate Al/Si, mixtures thereof, among other materials including clays (e.g., bentonite, montmorillinate, talc, etc). This layer can also function as an electrical insulator between the steel of the core/rotor laminates and the adjacent aluminum. By xe2x80x9celectrical insulatorxe2x80x9d it is meant that the layer has an electrical resistance of greater than about 1.0 milli-ohm (or a conductivity of less than about 1.0 milli-ohm). By xe2x80x9cadjacentxe2x80x9d as used in this specification and the claims, unless expressly stated otherwise, means two components or layers that are in contact with each other, are next to each other with a space separating them, or are next to each other with a third component or layer in between.
In another aspect of the invention, the coating composition further comprises iron nano-particles. The nano-particle containing composition, e.g., within a carrier comprising a water soluble polymer, can be incorporated within any suitable porous article. Examples of such porous articles comprise electronic components, magnets, shaped powdered metals, among other articles. If desired, the porous article (after being impregnated) can be heated.
The coating composition can also impart corrosion resistance to the surfaces of the rotor, e.g., the exterior surface of the rotor. That is, the coating composition reduces, if not eliminates, rotor corrosion that can occur prior to being contacted with aluminum.